Some propulsion-generating vehicles include multiple axles that are rotated by one or more motors to rotate wheels connected with the axles and propel the vehicles along a route. For example, some rail vehicles include motors that work to rotate axles of the rail vehicles to move the rail vehicles along a track. Each motor may separately rotate a different axle of the rail vehicle. In a locomotive, this can involve eight motors separately rotating eight different axles to separately rotate eight different sets of wheels. Each axle and motor being controlled by its own motor speed control device (motor speed controller and inverter). The individual rotation of each axle by a different motor controller (inverter) allows for greater control over movement of the rail vehicle, increasing overall ability to maximize traction, but also significantly adds to the expense and complexity of the vehicle.
Conversely, some vehicles include motor speed controllers that each control multiple axles. For example, a locomotive may have two motor speed controller that each controls three axles of each truck of the locomotive. While this reduces the cost and complexity of the vehicle, it also can reduce the performance of the vehicle. During movement of the vehicle, a single axle may slip due to a loss in traction between the wheels coupled with the axle and the surface being traveled upon. Because multiple axles are being driven by the same motor speed controller, the loss in traction for one axle results in the tractive effort generated by the other axles driven by the same motor speed controller to be also significantly reduced. This can be referred to as these other axles de-rating. Additionally, if an electrical problem such as a short circuit occurs, the problem can result in a loss of power to all axles coupled to the same motor speed controller.